Atom transfer radical cyclization (ATRC) applied to a chemoenzymatic synthesis of Quercus lactones

The natural fragrances (+)-trans whisky lactone 2 and (+)-trans cognac lactone 4, together with a minor amount of their (-)cis stereoisomers, were prepared in 50% and 42% overall yield, respectively, starting from racemic 1-hepten-3-ol (+/-)-5 and 1-octen-3-ol (+/-)-6. The procedure involved first the enantioconvergent, lipase mediated transformation of the secondary allylic alcohols derived dichloroacetates (+/-)-7 and (+/-)-8 into the corresponding homochiral (+)-7 and (+)-8, combined with their cyclization under a transition metal catalyzed atom transfer process. (c) 2007 Elsevier Ltd. All rights reserved.